Polarity-Induced Reactive Wetting: Spreading and Retracting Sessile Water Drops.

Area of Science:

• Surface Science
• Materials Science
• Physical Chemistry

Background:

• Wetting is defined by surface tension, often assuming invariant surface properties.
• Complex wetting involves time-dependent interfacial energy variations.
• Adaptive or reactive wetting processes are not fully understood.

Purpose of the Study:

• Investigate adaptive wetting using chemically heterogeneous surfaces.
• Tune hydrophilic-like wettability on perfluoroalkyl-silica-polydimethylsiloxane.
• Model time- and space-dependent reactive wetting.

Main Methods:

• Fabricated surfaces with low-energy perfluoroalkyls and high-energy silica moieties on polydimethylsiloxane.
• Tuned wettability through sequential deposition.
• Observed drop contact behaviors and contact angles.
• Modeled reactive wetting using first-order kinetics.

Main Results:

• Surfaces exhibited tunable wettability, from hydrophobic to rapidly spreading.
• Increased perfluoroalkyl deposition led to greater hydrophilicity.
• Chemically heterogeneous surfaces demonstrated wetting-reactivity.
• Abrupt wetting transitions showed unique decreasing advancing and increasing receding contact angles.
• Reactive and recovery mechanisms were identified.

Conclusions:

• Chemically heterogeneous surfaces are inherently wetting-reactive.
• Time- and space-dependent reactive wetting can be modeled with first-order kinetics.
• Reactive and recovery mechanisms govern dynamic wetting behaviors.